1. Field of the Invention
This invention relates to heat exchangers, and more particularly, to an evaporator or a condenser for use in an automotive air conditioning refrigeration circuit.
2. Description of the Prior Art
Heat exchangers for use in automotive air conditioning refrigeration circuits, such as evaporators or condensers, are known in the art. Referring to FIG. 1, a heat exchanger for use in an automotive air conditioning refrigeration circuit, such as serpentine-type evaporator 10 is shown. Evaporator 10 includes continuous serpentine flat tube 11 through which refrigerant fluid flows. Serpentine tube 11 includes a plurality of spaced, parallel planar portions 12 and a corresponding plurality of curved connecting portions 121. Air flows through evaporator 10 between planar portions 12 in the direction of arrows "A" as shown in FIG. 1. As shown in FIG. 2, the interior space of serpentine tube 11 is divided by a plurality of parallel partition walls 111 into a corresponding plurality of essentially parallel passages 112, through which refrigerant fluid flows.
Serpentine tube 11 has two terminal ends and is provided with inlet mechanism 15 and outlet mechanism 16 at its first terminal end 11a and second terminal end 11b, respectively. Inlet mechanism 15 is linked to the output of a compressor or other suitable compression means (not shown) of the refrigeration circuit through a connecting pipe member (not shown), and outlet mechanism 16 is linked to an inlet of the compressor through another connecting pipe member (not shown). Refrigerant fluid flows into serpentine tube 11 from the compressor via inlet mechanism 15, flows through each successive planar portion 12 and connecting portion 121 towards outlet mechanism 16, and is then returned to the compressor. The refrigeration circuit may include other elements disposed between the compressor and evaporator 10.
Inlet mechanism 15 includes a cylindrical header pipe portion 151 and a separate cylindrical conducting pipe portion 152. Header pipe portion 151 is designed so that its inner diameter is slightly greater than the outer diameter of conducting pipe portion 152. Header pipe portion 151 is further designed so that its length is slightly greater than the depth of serpentine tube 11, wherein depth is the lateral dimension of tube 11 taken in the direction of airflow "A". Furthermore, header pipe portion 151 has a clad construction in which the inner peripheral surface of header pipe portion 151 is fixedly covered with a brazing metal. Conducting pipe portion 152 is bent to have a generally U-shaped configuration so that conducting pipe portion 152 includes integral first, second and third straight regions 152a, 152b and 152c. Second and third straight regions 152b and 152c of conducting pipe portion 152 are parallel to each other. One end of 152b and one end of 152c are connected at right angles to the opposite ends of first straight region 152a, respectively. The length of second straight region 152b is shorter than third straight region 152c. The end of third straight region 152c, which is disposed opposite from where it is connected to first straight region 152a, is bent downwardly at a right angle. Union joint mechanism 153 is provided at this other end of third straight region 152c of conducting pipe portion 152 allowing it to be connected to one end of a connecting pipe member (not shown).
Cap member 154 also has a clad construction and is provided at the upstream opening end of header pipe portion 151 which is located at the upstream or air inflow side of evaporator 10, and is fixedly and hermetically connected to the upstream opening end of header pipe portion 151 by brazing. The first terminal end 11a of serpentine tube 11 is inserted into the inner hollow space of header pipe portion 151 through a slot (not shown) formed at the lower or bottom region of header pipe portion 151, and is fixedly and hermetically connected thereto by brazing so as to allow fluid communication. The end of second straight region 152b, which is located opposite the end connected to first straight region 152a, is slightly inserted into the inner hollow space of header pipe portion 151 through the other opening end of header pipe portion 151, located at the downstream or air outflow side of evaporator 10, and is fixedly and hermetically connected thereto by brazing so as to allow fluid communication.
Outlet mechanism 16 includes cylindrical header pipe portion 161. Cap member 162 is provided at the downstream opening end of header pipe portion 161 located at the downstream or air outflow side of evaporator 10, and is fixedly and hermetically connected thereto by brazing. At approximately the middle (i.e., lengthwise) of header pipe portion 161, which is located at the upstream or air inflow side of evaporator 10, the header pipe portion 161 is bent downwardly at a right angle, and the region of header pipe portion 161 located at the upstream opening end is bent horizontally inwardly at a right angle, i.e., bent at a right angle such that the main axis of this end portion is perpendicular to the planes of parallel passages 112, with the upstream opening end of header pipe portion 161 oriented facing toward the plane of the parallel passages 112 having the first terminal end 11a. Union joint mechanism 163 is provided at the upstream opening end of header pipe portion 161, allowing it to be connected to one end of another connecting pipe member (not shown). The second terminal end 11b of serpentine tube 11 is inserted into the inner hollow space of header pipe portion 161 through a slot (not shown) formed at the bottom or lower region of header pipe portion 161, and is fixedly and hermetically connected thereto by brazing so as to allow fluid communication.
Evaporator 10 further includes corrugated heat receiving metal sheets or fin units 13 disposed between opposed planar portions 12. Fin units 13 are fixed to planar portions 12 by brazing along the lines of contact. Protective side plates 14 are fixed to the exterior side of each of the outside fin units 13. Fin units 13 enhance the heat exchange between the air flowing through evaporator 10 and the refrigerant fluid flowing through serpentine tube 11.
During operation of the automotive air conditioning refrigeration circuit which includes evaporator 10, refrigerant fluid is provided to serpentine tube 11 from the compressor via a connecting pipe member, conducting pipe portion 152 and header pipe portion 151 of inlet mechanism 15, and then flows through each successive planar portion 12 and connecting portion 121 of serpentine tube 11 towards header pipe portion 161 of outlet mechanism 16, and is then returned to the compressor via the other connecting pipe member. When the refrigerant fluid flows through each successive planar portion 12 and connecting portion 121 of serpentine tube 11, the heat exchange between the air flowing through evaporator 10 with the refrigerant fluid flowing through serpentine tube 11 takes place. Thus, the air flowing through evaporator 10 is cooled by vaporization of the refrigerant fluid, and there is absorption of heat from the air to the refrigerant fluid. The cooled air leaving evaporator 10 is conducted into the passenger compartment of the automobile to air-condition the passenger compartment.
Because the second straight region 152b of conducting pipe portion 152 of inlet mechanism 15 is connected to the downstream opening end of header pipe portion 151, located at the air outflow side of evaporator 10, the refrigerant fluid conducted into conducting pipe portion 152 flows through the inner hollow space of header pipe portion 151 from the air outflow side to the air inflow side of evaporator 10. Refrigerant fluid flowing through the inner hollow space of header pipe portion 151 is distributed into each of the plurality of essentially parallel passages 112 defined in serpentine tube 11. The refrigerant fluid flows into each of the plurality of essentially parallel passages 112 in a non-uniform distribution pattern such that the amount of the refrigerant fluid flowing into each of the plurality of essentially parallel passages 112 gradually decreases from the air inflow side to the air outflow side of evaporator 10.
Since the refrigerant fluid flows into each of the plurality of essentially parallel passages 112 in a non-uniform distribution pattern, the air immediately flowing into evaporator 10, having a relatively high temperature, exchanges with the refrigerant fluid having a relatively large flow amount in passages 112 located at or near the air inflow side of evaporator 10. Accordingly, the heat exchange between the air flowing through evaporator 10 with the refrigerant fluid flowing through serpentine tube 11 is effectively carried out.
While the prior art evaporator has the advantage of its heat exchanging performance as described above, the prior art evaporator has a disadvantage in its construction as described in detail below.
As illustrated in FIG. 1, second straight region 152b of conducting pipe portion 152 of inlet mechanism 15 extends straight out from the downstream opening end of header pipe portion 151 located at the air outflow side of evaporator 10 so that the overall depth of evaporator 10 is unavoidably increased in an amount approximately equal to the length of second straight region 152b of conducting pipe portion 152. Moreover, the length of second straight region 152b must be long enough to allow conducting pipe portion 152 to be satisfactorily bent to form second straight region 152b. Therefore, the overall depth of the prior art evaporator can not be sufficiently reduced to allow the evaporator to be installed in an automobile where the interior space available to accommodate the evaporator is necessarily restricted.